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Is it possible that meteor could strike a commercial airliner?
Is it possible? Are there some such accidents in human history? Is there any rules or systems design to protect airplanes?

Interesting followup question: did a meteor ever hit a comet?

of course it's possible. why would it not be possible? perhaps you should revise your question title to reflect the other questions you've asked.

Is it possible to win the lottery, get struck by lightning, and attacked by a shark on the same day? Is it possible to discover the cure for Alzheimer's, US immigration policy, and the Isreali/Palestinian conflict at the same time?

No, that's impossible. There is a special, meteorite-proof force field around all aircraft that prevents them from being struck by extraterrestrial objects.

While the question is definitely specific, it seems to be a very good one, as meteors are very numerous at low altitude (and the ones that hit the ground too). Their speed is very high in space (e.g. 7 km/s), but quickly decreases, that's the point. Space launches and astronaut protection take this into account. So what needs to be explained is the difference between space and ground as regards to meteors.

Earth is HUGE compared to a plane. It's roughly equally likely for a specific plane to be hit as for a meteor to land within 40 meters of a randomly chosen spot on the world.

Earth has many cows, and they spend a long time outside; and yet, there are only two documented cases of cows being hit by meteorites, one in 1972 (cow dead and charred), and another in 1938 (minor injures).

@NateKerkhofs The question was not about the odds of a specific aircraft, but about an aircraft being hit (specifically a commercial airliner).

@Lnafziger I had no clue how many aircraft there are flying in the air at all times on average at the time of the question. I did some research now, and I'm planning on giving a more accurate direct answer to the question.

@mins ISS is a lot more likely to get hit by a meteor than an airplane. It doesn't have the benefit of the vast majority of meteors burning up in the atmosphere before hitting it. And all but the largest ones would impact the ISS at much higher speeds than they would an airliner (and, with the largest ones, either the airliner or the ISS would be toast.)

@mins Ah, ok. That comment was about airplanes, though. Look at the links. :)

@reirab: Ah! I've got everything wrong, and the comment was indeed a nice one :-)

@NickT: It is physically impossible to resolve the Israeli/Palestinian conflict.

A meteorite could hit an airplane, sure. There's no known cases of it happening because meteorites which survive atmospheric entry are very rare, and airplanes are pretty small so the likelihood of it happening is extremely low.

Is there any rules or systems which protect airplanes?

@kharandziuk Meteorites usually fall under VFR, so they are see and avoid. What rules or systems do you have in mind?

There's no defense against meteorite strikes on aircraft besides their structural strength.

Under "rules" I mean something similar to rules about weather(don't fly in storm). Is there any regulation about meteorites? Is there any meteorite forecasting?

Since we are talking about infinitesimally small probabilities, we should also be infinitesimally anal, I think :-D So, no, it is not possible for a meteorite to hit an airplane, unless the airplane is buried underground, because a meteorite only becomes a meteorite after hitting the ground. Before that, it is first a meteoroid, then when it enters the atmosphere, it becomes a meteor.

It's very rare that we know about meteor strikes in advance and when we do we only have a general area where they may strike. Pilots are warned in that case and can choose to avoid that area. It's very rare that happens, the vast majority of meteor activity is not predicted.

Thousands of tonnes of meteorites hit the Earth every year.  We may think it's densely populated, but the chances of a meteorite hitting a populated area are tiny and even if it did, would anyone notice?  The chances of hitting an aircraft are so small as to be completely ignored.

@JörgWMittag Even more infinitesimally anal.  I would refine the defintion as "becomes a meteorite when it hits something.  If a meteor struck a tree and embedded itself, would you still call it a meteor?

@Simon I think saying that a tree is part of the Earth's surface for the purposes of distinguishing between a meteor and a meteorite is reasonable.  And I don't know that it's "anal" or pedantic to ask people writing what we hope to become reference questions to use correct terminology.

@MontyHarder Would it still be a meteor or become a meteorite if it struck and lodged itself in a flying airplane?

@MontyHarder Of course it is.  Common usage will trump a formal definition every time outside of the professions.  A meteor can only be a meteor in free flight through the atmosphere.  It was supposed to be a liltte jocular word play to lighten the comments.

"meteorites which survive re-entry" If it doesn't survive, it's not a meteorite. And meteors don't "re-enter": they "enter".

Meteorites which survive re-entry are especially rare when compared to meteorites which survive initial entry.

@JörgWMittag: Of course a meteorite could hit a plane! If I picked it up and threw it at it. ;-)

@JörgWMittag A meteoroid never becomes a meteor, it causes a meteor. Meteor is the name for the atmospheric phenomenon.

@JörgWMittag actually, you're being astronomically (as in hugely) anal. To be infinitesimally anal is to barely be anal at all.

I think chat is a better place for this gents.

Yes, it is possible, however unlikely!

The final report into the downing of MH17 investigated the possibility that the aeroplane was hit by "meteor or space debris"

In section 3.5 a number of scenarios are analysed that relate to the possible source or sources of the object that perforated the aeroplane. These include meteor and space debris.

It was concluded that

The chance of a meteor striking an aeroplane was calculated as being one event in 59,000 to 77,000 years. This value was obtained from the University of Pittsburgh's Department of Geology and Planetary Science and was originally part of the NTSB's investigation into the 1996 accident to TWA flight 800 (see NTSB Report AAR-00/03, dated 23 August 2000)

one event in 59,000 to 77,000 years - and the odds of it bringing down an aircraft even if "perforated" - 1,000 to 1 or something equally small.  So chances of being hit by a meteor bringing down an aircraft, in the hundreds of thousdands of years.  Most meteors are the size of grains of sand or very small pebbles.

@Simon I guess the chance would be comparable to dropping a ball bearing from a 747 and hitting, say, an egg sandwich (Douglas Adams)

Big Sky wins again.

@sanchises surely such an event would be Infinitely Improbable?

@mikeTheLiar merely virtually impossible...

It would be useful to have the probability of winning the lottery alongside as a comparison!

@Joze how about lightning vs lottery? #shamelessplug

@Jamiec Then I guess what I want is, in summary what is the chance that the meteor strikes an aircraft?

Some of the other answers attempt to come up with a figure for that.

When I served at a military airport in Hungary I read a written report of a MIG-21, supposedly hit by meteor or space debris, crashing the cabin canopy. It was flying with afterburner at high altitude and the pilot's hand was on the throttle lever waiting for instructions. This is why he could manage to slow down and survive. Not an airliner though.

OK, I've been asked to create a "guesswork" answer.
Assumptions.

75% of flights are made during daylight hours.
75% of meteors occur at night for any given location and those meteorites are equally likely over half the worlds surface (probably about 25% overestimate).
Aircraft distribution is uniform across the Earths surface (this will make my esimate incorrect by orders of magnitude since they are not, they are far more densely packed over the US, Europe and SE Asia)
Number of aircraft in the air during the time when the 75% of meteors occur, 2,500.
Average speed of meteorites, 80,000 mph.
Average surface area of aircraft, 300 m².
If a meteor hasn't burnt out by 7 miles, it's not going to (it's a meteorite).
350 meteorites per day.

Ignoring the height for now.
Total surface area of aircraft flying when the 75% of meteors fall. 750,000m².
% of Earth surface where the 75% fall covered with aircraft.  0.000003%.
Chance of any meteorite hitting the target surface area (an aircraft).  0.00105%.
Now factoring in height.

Depth of atmosphere where aircraft are found.  7 miles.
An aircraft presents a target 150 feet high - big overestimate to account for the time the nose of the aircraft to the tail passes through the track of the meteorite.
Ignoring that the meteorite will slow down as it passes through the atmosphere.

Assuming a meteorite will pass where the aircraft will be, it spends 0.0036% of the time it falls at the height of the aircraft.
Multipyling the chance of it hitting the area described by the aircraft by the chance of it being at the same height in that area - 0.000000378% or about 4e-7.
Many people struggle to understand numbers that small.  To put it into perspective, the accepted chance of you being struck by lightning in your lifetime is 8e-5, or about 200 times as likely as an aircraft being hit by a meteorite.
This is so tiny that any one of my assumptions being wrong will make the number meaningless.
Safe to say, possible, but so unlikely as to be not even worth considering.

"75% of meteors occur at night" - sorry, that raised a couple of warning flags for me. What? Why? What have meteorites to do whether there is night or day? Do you have a credible source? Isn't just that meteorites are more visible during the night?

@vsz Most meteors occur because the Earth passes through a cloud of particles.  Therefore, most come from the direction the Earth is passing through space.  You could start here for more information.

@reirab Because 350 meteorites fall during the time 2500 aircraft are airborne?

Thanks for doing a full answer and covering the 3D dimension.

@mins Agreed.  Edited.

I'm really not trying to be annoying, but what exactly has a probability of $4 \times 10^{-7}$? Is it any plane on a given flight? Or any plane in one year? Or any plane in an average lifetime? Or something else? The reason I'm asking is that once we know, we can calculate the collision rate...

@OwenBoyle  Last comment on probabilities, then I suggest you ask on Math.SE.  You are talking about sequences and sets, not distributions.  If I throw a 6, then the probability of me throwing a 6 next time is still 1/6.  If the probability of a meteorite hitting an aircraft is x at time y, then it is still x at time y+1.

@OwenBoyle The probability of it happening in any one day, since it is the number of meteorites per day and the number of aircraft airborne that I used in the guesswork.

@Simon OK - I actually got less than that! (Re probability: obviously the probability per trial is constant. I never said it wasn't. It is the probability that it has ever happened that rises with time. Is it better to buy two lottery tickets, or one?

Possible, but unlikely. There are no documented instances of a meteorite striking an airplane.
Most of the meteoroids that become meteors are of the size of a grain of sand, and will burn up by the time they reach the cruising altitude of the commercial airliner.
A hundred or so meteors of the size required for impact at high altitudes strike earth every hour. At the terminal velocity of the meteors, the aircraft is practically stationary and the probability of a meteor striking an aircraft is simply the ratio of the total area of aircraft in air to the total surface area of earth.
Around 4000 aircraft are in skies at any given time- each with a projected area of ~300 $m^{2}$ (if we are being generous). This means that the probability of an aircraft getting hit by a meteor is ~$2 \times 10^{-9}$ at any point of time.
Assuming that each aircraft makes a 8 hour flight (again, being generous), the probability of that getting hit by a meteor is ~$10^{-6}$.
So, basically the probability of an aircraft getting hit by a meteor is pretty small; Again, if we continue to operate aircraft at the rate we do, one of them will certainly get hit by a meteor.

Your logic is flawed.  Most meteroids enter the atmopshere from more or less the same direction, that is to say from the direction in which the earth is travelling.  That's why meteor showers appear to radiate from the same point in space and named after whatever arbitrarily named object they appear to emenate from.  one of them will certainly get hit by a meteor.  This is also flawed.  Even if it hasn't happened, then it is not "certain" that it will and it may well have already happened.  Probablilities know nothing of history. If it happened 1 second ago, the probability remains the same.

Because the Earth does not travel towards the sun, most meteors occur at night when air traffic is a lot less.  You also assume that aircraft are evenly distributed but they are not.  They are concentrated in a few areas of the world during the day. You would need to build a much more complex model to begin to guess at a probability but it's a lot lower than you suggest. It may already have happened when some puzzled engineer could not figure out what that hole in the horizontal stabiliser was and just fixed it up with no report to file.

The answer is a good back-of-the-envelope calculation to get the order of magnitude and demonstrate just how wildly unlikely it is. It's basically the Big sky theory. The probability is likely a lot lower because the calculation should be done for three dimensions (plus time), not two. The distribution of aircraft in the sky does not matter if we assume meteor paths are random (ie. that they have no preference for high density air travel lanes).

@Schwern Of course the distribution matters.  Did you read my comments?  The majority of meteors come from the front of the Earth as it travels through space.  Very few come from other angles.  Since the majority, at any one time, happen over something like a quarter of the Earths surface and at night, the distribution is perhaps the most important factor in any guesswork.  Since most aircraft are clustered in a few areas during the day, then most aircraft are not in the area where most meteors occur.

Umm.. The "front" of the Earth is the dawn terminator. So a meteor approaching from the front has a 50:50 chance of hitting Earth on the day-time or night-time. You might get a factor of 2 into the equation but the Answer's logic is far from flawed. What is flawed is your comment about probability - the question is not whether the probability in a particular instant increases with time; it is whether the probability of an event happening at all increases with time. This is certainly the case.

Given your 300 m^2 assumption, one aircraft represents a fraction of about 5.8 x 10^-13 of Earth's surface. Assuming 8 hours and 100 meteors/hour, that's a 4.7 x 10^-10 hit probability for that particular aircraft on that flight, not 10^-6. The 2 x 10^-9 number is the chance of a given meteor hitting any aircraft, not that particular one. At 100 meteors/hour, that's a 2 x 10^-7 probability of any aircraft being hit in a particular hour, meaning that we'd need to go 1,142 years before the probability of any aircraft being hit reaches 50%.

Actually, longer than that. I forgot to subtract the probability of more than one incident occurring in that time. At any rate, you get the idea. It's very improbable.

@Simon I was referring only to the distribution of planes into travel lanes, but a map of meteor strike density would help. Your point about more meteors hitting at certain times of day is sort of true, but if there's less planes when there's more meteors (at night) and vice versa then the difference might even out. Let's make it clear we're talking about the chance of any plane being hit. The chance for a given plane to be hit would change depending where it is on the Earth. Anyhow, I don't think it's going to throw off this back-of-the-envelope calculation by an order of magnitude.

@OwenBoyle It certainly does not.  The chance of a random meteorite hitting a random place or object is a geometric distribution, not exponential.  The chance of it happening in the next second is identical to it happening in the last second.  It does not get more likely.  The chances of a geometric event occuring do not increase because the event has not occured x times.

@OwenBoyle Nope.  Most meteors occur after midnight for any given location.  One of many explanations why - http://www2.le.ac.uk/departments/physics/research/xroa/astronomical-facilities-1/educational-guide/meteorites

@Schwern There is no "vice-versa" since you do not get most meteors in the location where there are most planes. It is a fact that most meteors occur between midnight and dawn.  It is a fact that there are far fewer aircraft between midnight and dawn.  The calculation in this answer woefully overestimates the odds and is therefore useless - not a "useful back of the envelope calculation".

@Simon You get the most planes when there are the least meteors and the least planes when there are the most so it might cancel out... maybe. I think we all agree this answer is just a rough estimate and can be revised to take more factors into account. This comment thread is getting very long, how about you write up an answer?

@Schwern I think Simon's point was that both of those factors work against the probability of a given meteor hitting any airplane, rather than balancing each other out. That is, most meteors will fall on the opposite side of the Earth from most airplanes, making a strike much less likely than if either the meteors or the airplanes were distributed uniformly across Earth.

@Simon: After midnight lasts right up until noon the next day. If you sit on the Earth's orbit watching the Earth looming up on you, you see a half-full Earth. So if we assume meteors only come from the "front", it's 50:50 whether it's day or night (don't assume because we can't see them in day-time that they're not there).

@Owen Please read the link I included, from a world authority, on why most occur between midnight and dawn.  If that doesn't satisfy you, please let me know and I'll dig out some more.  As an amateur astronomer, I am well aware that meteors occur during the day.

@Simon: Re probability: We're not asking the probability of a particular plane being hit by a particular meteor - that is obviously constant. We're asking the probability of a hit eventually happening - clearly that rises with number of tries. Look at it this way: if you throw a dice once, the odds of a six are 1/6. If you make two throws, the odds of at least one six are 11/36.

This is, sadly, a highly topical question. There have been more than a few aircraft downings where a meteor impact has at least been considered so I think it is worth exploring.
Acknowledgment: In the following calculations have gratefully borrowed figures from various contributors above.
First, let's consider the question about traffic patterns:

Meteors mainly come from the direction Earth is travelling through space as it orbits the sun (effectively, the Earth "runs them down").
Meteors are in orbit around the sun before they hit Earth. So they are just as likely to come from inside the Earth's orbit (on the way out from the Sun) as from outside the Earth's orbit.
This means they mostly occur between midnight and noon the next day. From noon to midnight, you're on the "rear end" of the Earth.
I'm assuming traffic density between midnight and noon is roughly the same as between noon and midnight. This cancels out any effect of diurnal variation in traffic patterns. If you disagree with this point, divide the answer by two or three.

Second, I am going to integrate over a 24hr period to cancel out the variation in aircraft density as the "front" of the Earth moves round the planet (there are going to be more targets when Europe, North America and SE Asia are at the front than when it's dawn over the central Pacific Ocean).
Third, the aircraft speed is irrelevant. If a beetle is on a dartboard and you randomly throw a dart, it doesn't matter if the beetle stays still or runs about.
Now to the sums: To be clear, I'm trying to work out the probability of any meteor hitting any aircraft in a 24 hour period. This is simply the area of the target divided by the total area presented by the Earth to the oncoming meteor.
So: 10,000 planes in the air divided by 2 (only the leading half of the Earth is in target) $\times$ 300$m^2$ per plane divided by $\pi r^2$ for $r=6371km$ gives $1.2 \times 10^{-8}$. So one in a hundred million, roughly.
Now, how many meteors that could down a plane, hit the Earth per day? Planes are pretty fragile - I'm going to guess that a 0.2m bolide (bowling ball?) if it hit the plane anywhere, would definitely do it. One reference above says there are about 2000 of these per year. So 5 per day.
That gives a final probability that any plane is downed by any meteor in any 24 hour period of $6 \times 10^{-8}$.
So the rate is about once every 40,000 years, or so. Yeah... probably not worth bothering about.

You're not that far away with your "back of the envelope" than a whole bunch of experts (see my answer)

Believe it or not, I only read the numbers in the yellow quote-box after I'd finished this calculation. Another way of putting it is that there's about a 1000:1 chance of it ever happening anywhere in the next 50 years.

I see that someone else did the math on the probability already, but I wanted to give some math with dimensions and numbers that might be more accurate, as well as give a comparison to other causes of plane crashes.
At any point in time, there are about 10,000 commercial aircraft in the air, according to flight radar's metrics (although I'm not too sure how accurate those are). Assuming an average length of 50 meters, and a wingspan of 50 meters, and a hull and wing width of 8 meters, that's 800 m² per flying aircraft, and 8,000,000 m² for all planes combined, or about 8 km².
In a comment, someone pointed out that aircraft dimensions are actually closer to 200 m². The reason I chose math of 800 m² is because a direct impact is not the only way a meteor could affect an airborne craft. A sufficiently big meteor leaves behind a heat trail and a smoke trail. The heat trail causes local airflows to change, which could cause turbulence onboard passing aircraft. The smoke trail could theoretically damage the engines similar to how volcanic ash does, given that they're both ash and dust. If a layman is on an airplane affected by one of these incidents, it's understandable that they view this as "being hit by a meteor".
How big is 8 km²? Well, that is comparable to the size of Greenbelt park in Staten Island, and about 2/3 the size of the Royal Borough of Kensington and Chelsea in London. I've tried finding reports of meteorites being found in that area, and while it is not impossible that one has landed there without anyone noticing, it is a very rare event. In fact, while there hasn't yet been a report of a plane crashing by a meteorite, a passenger killing both the captain and the copilot has been reported at least twice as the reason of a crash. I would personally be more worried about a mid-air impact of another plane, given that has happened enough by now to be featured multiple times on Mayday! (Air Crash Investigation).
If you only count direct impacts as actually hitting your aircraft, then assuming an average surface of 200 m² for a plane, and meteors only coming directly from above (since they can also come from the front, the sides or the back), there is a total surface size of about 2 km² when all aircraft are counted. This is a little smaller than the City of London (not the entirety of London, but the original inner city), or just over half the size of Central Park in New York.

The OP didn't said this is something frequent. Only asking if this could be possible. As for your claim that meteorite impacts are rare... have a look at the Antarctic Meteorite Program: "Of the almost 16,000 Antarctic meteorites collected since 1976, over 14,000 have been permanently transferred to the Smithsonian." Only the ones collected!

@duskwuff. It sometimes snows, also in Antarctica (about 15 cm per year), but agreed. The (estimated indeed) actual mass of meteorites is about 50.000 tons each year. Discarding very small particles: "Over the whole surface area of Earth, [...] 18,000 to 84,000 meteorites bigger than 10 grams per year".

@mins Antarctica has been an icy shelf for over 15 million years. About 5500 meteors hit Antarctica every year on average according to http://jdetrick.blogspot.be/2013/12/how-many-meteors-hit-us-each-year.html and doing some math on that. That includes those that burn up in the atmosphere. Antarctica is about 1/36 of the Earth surface, so by your math, 500-2500 meteorites should hit it every year. Over a period of a thousand years, that's about 500K-2.5M meteorites. I didn't say they were rare, I said they were rare if we're talking about an 8 km² area.

Ok Nate, I agree with you.

While the numbers in this estimate are probably the right order of magnitude, 8 m is a vast overestimation of the average width of the average airliner fuselage. The vast majority of airliners are 737 class and smaller. A 737 has a fuselage width of 3.76 m. According to this source, the wing area of a 737-700 is 124 m^2. The projected area of the fuselage will be a bit less than 3.76 m x 32.18 m = 121 m^2 (less because it narrows in the front and back.) So, the average area is probably somewhere in the ballpark of 200 m^2.

@reirab  You're correct in case of direct impact. I assumed a hull width of 8m because even a close encounter that doesn't hit can put the plane in jeopardy. The meteor really heats up the air directly around, causing wind flows that can affect the plane similarly to turbulence. In addition, the smoke and dust that is generated because of the meteor burning up in the atmosphere might affect the engine in a similar way to volcanic ash, given that they're both made of rock and debris particles. Both of these effectively increase the surface area at which a plane might be affected by a meteor.

@reirab In case of just counting direct impact, the impact area for all planes worldwide is closer to 2 km², which is about the size of the City of London.

@NateKerkhofs Ah, alright. However, in order for any of those factors to actually matter, it would probably have to be a much larger than average meteor (and the shockwave might be the biggest problem in that case.)

@reirab Another thing to take into account is that a meteor can technically also hit from the front, back or sides, not just from above.

@NateKerkhofs Right, but then the probability will be based on the projection of the aircraft into whatever plane is orthogonal to the flight path of the meteor, which will at most be a bit larger than the projection into the horizontal plane and more frequently somewhat smaller.

@reirab This is getting into discussion territory, but I will say that the probability across the entire airline fleet globally has nothing to do with the direction the meteor is travelling. At any point in time, any plane can be hit from any non-bottom angle by any meteor. The speed and direction of the airplane has little to do with that. A hit is a hit regardless.

It could happen. This lucky skydiver was only meters from a falling space rock, and got it on tape.
Had he been an airplane (or a few meters longer) he would have been hit!

Except it's not - http://news.discovery.com/adventure/extreme-sports/mysterious-object-in-skydiving-video-identified-140410.htm

While the scientist involved thinks it's a true story, other scientists are more skeptical. Note that, technically, based on the scientist declaration about the origin, it's an asteroid from the asteroid belt, not a meteor (comet debris).


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How does a pilot tell passengers to prepare for severe turbulence without causing panic?
At the start of a flight, the pilot of an aircraft often talks about the expected weather on the flight path, and tells passengers if there is to be some turbulence during the flight.
How does a pilot explain that there will be severe turbulence to their passengers without inciting panic?

Usually they try to route around it, but if it pops up, I often hear "Ladies and gentlemen I've turned on the fasten seat belts sign and asked the flight attendants to be seated, we may be entering an area of turbulence and would like everyone seated for safety" or something to that effect.

So in your opinion they would never explicitly say whether or not it will be severe turbulence?

I've only personally heard a pilot say it once, ATC is usually pretty good about rerouting around turbulence, severe turbulence enroute is usually detected through PIREPs from aircraft ahead and if severe, other aircraft are routed around it pretty quick.

The key is "I've asked the flight attendants to be seated", it would be pretty severe to stop service.

No real chance to panic since you are holding on for dear life. I had an emergency landing- no real difference to extreme turbulence. They just put seatbelt lights on several time and dim lights and maybe get cabin crew to emphasize sitting down.

Despite what you see in films; people actually rarely panic in response to such situations

@user2617804 Huh? An emergency landing is completely different from extreme turbulence. Most emergency landings are just landings; extreme turbulence throws unrestrained objects around the cabin and worse.

@RonBeyer Not really. Moderate turbulence (per the FAA's definition) is usually enough to stop the service in my experience. I've never been in what I would consider 'severe' turbulence, but I've been on many flights where the FAs were told to pause service and sit down.

I always use the FAs as a sign. If they're sitting, its time to make sure everyone is ready for severe weather

@DavidRicherby: That's severe turbulence.  Extreme turbulence throws the entire aircraft around.

Turbulence is reported on a scale of light, moderate, severe, and extreme.  The full definitions are available in the FAA Aeronautical Information Manual. As experienced in the cabin,

For Light Turbulence, "Occupants may feel a slight strain against belts or shoulder straps. Unsecured objects may be displaced slightly. Food service may be conducted and little or no difficulty is encountered in walking."
For Moderate Turbulence, "Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult."
For Severe Turbulence, "Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about. Food service and walking are impossible."
Extreme Turbulence is "turbulence in which the aircraft is violently tossed about and is practically impossible to control. It may causes structural damage."

As a pilot, once the ride gets to the point of light turbulence (and not just light chop), I'll probably ask the flight attendants to go ahead & sit down.  Even though they might be able to serve, I don't want them out in the middle of the aircraft if things get worse & then they'd have nowhere to sit.  That may not be a PA announcement; I may just call them on the interphone & say something to the effect of, "ATC says this is probably going to last for a while, so why don't you guys go ahead & take your seats for a bit."  If we find out that the ride is about to get bad soon & suddenly, that's when I'll typically use the PA and be more directive: "Flight attendants, take your seats; flight attendants please take your seats."
In moderate turbulence, there's no question but that everybody needs to be sitting down.  And I'll be looking for better options (typically, changing altitude) in order to get a better ride.  Sometimes a better altitude is available, and some times you just have to ride it out.
I won't intentionally fly into severe turbulence.  If I know before takeoff that the only way to complete the flight is to transit an area of severe turbulence, I won't take off.  If it's possible to work out a different routing and/or altitude(s) that avoid all the areas of known & forecast severe turbulence, then we can plan on that, but you won't find me ever explaining to passengers before the flight that we'll be flying through severe turbulence today.  Not unless we're the last flight out of Saigon before it gets overrun by the murderous hordes, but I don't really foresee that scenario.
If you do fly into severe turbulence despite the best precautions, you've (hopefully!) already got everybody seated since you were probably expecting moderate turbulence anyway.  After landing, the aircraft will need to be inspected, because any encounter with turbulence classified as severe requires an inspection before the aircraft can fly again.  Typically, no problems are found (airliners are built pretty sturdy these days), but a mechanic will check all the things that might be over-stressed or damaged in that sort of an encounter in order to ensure that everything is still good to go fly again.
As far as preflight PA's when we're expecting light or moderate turbulence, that depends a little bit on the situation.  If it's a short flight with enough time in some sort of turbulence, I'll coordinate with the flight attendants ahead of time to not bother trying to serve, and then on the "welcome aboard" PA I'll explain that situation to the passengers.  The ride is forecast to be pretty bumpy, and so to keep our flight attendants safe, and since I'm sure nobody wants hot coffee spilled in their laps, I've asked our flight attendants to remain seated for the flight and not attempt any beverage service. So sorry, it's all about safety, thank you for your understanding, blah blah blah, and since they'll be staying seated, we do ask that you also observe the Fasten Seatbelt sign and remain seated for the short duration of the flight today as well."
If only a small part of the flight is expected to be turbulent, I probably won't say much about it at the gate (the Flight Attendants cover "stay seated while the seatbelt sign in on" at length), and then maybe as we're getting close, I'll mention something just to reinforce what they say on the PA.  But if there's nothing special to communicate, I don't see great value in creating apprehension before the flight about an interval of turbulence that we may end up avoiding altogether.
Some pilots to make it part of their preflight PA's to re-emphasize the Fasten Seatbelt sign and stress again that we want you seated when it's on.  That's an individual pilot's preference (at least at my company).  Our guidelines recommend against using the word "turbulence" because it does cause apprehension, and instead talk about a choppy ride or rough air or bumps in the road or whatever.  Conveys the same meaning to the passengers, while hopefully scaring the nervous fliers a little less.

Fantastic answer, thanks!

I love the PA announcements in airplanes, as a passenger; it is a nice murmur while I fall asleep in the incredibly comfy seats in the evening after a long workday. I got a nice chuckle around here in a train when the PA announced something just like on an airplane (using all the same language - the train folks used to talk much gruffier in the past). Thanks for giving that example in your answer, with "bumpy rides" and the "flight today" and such. :)

@AnoE I'm thinking if a train PA announced that it was going to be a bumpy ride, I'd be looking to get off before we left...

"Not unless we're the last flight out of Saigon before it gets overrun by the murderous hordes..." Thank you for taking that into consideration in your flight planning. :)

@FreeMan  There are all kinds of rules that can happily be bent when the alternative to leaving is sufficiently awful. One of the last C-130's to leave Saigon had something like 470 people on it; normal capacity is a little over 100. Nobody knew what the airplane weighed -- takeoff data was probably along the lines of "max power & rotate before you're out of runway." Pretty far out from normal ops, but necessary & appropriate to the situation they had. Airline ops generally don't remotely approach those sorts of contingencies.

@RalphJ I believe the last Hueys off the roof were seriously overloaded, as well. I enjoyed your wording and was mentioning that in (what was intended to be) a humerus way.

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text:
Why do the ailerons of this flying wing work oppositely compared to those of an airplane?
I made this simple wing glider and put some ailerons on it. I thought that the ailerons in this glider would work the same way it works on airplanes, wherein the roll will be in the direction of the aileron that is pulled up. However, the opposite happens. For example, when I pull the left aileron up and the right aileron down, instead of rolling to the left, it rolls to the right. What is the reason behind this? And what is the difference between the control of this flying wing to a conventional airplane?

Could you film it?

Silly question perhaps, but is the stick the nose, or the tail?

Just a wild guess (hard to tell from your picture) - the down aileron is likely adding a ton of drag to the right side.  Try bending it down 1/2 the amount you're doing now.

Not unrelated -- https://aviation.stackexchange.com/questions/47514/how-do-paraglider-controls-work , https://aviation.stackexchange.com/questions/47514/how-do-paraglider-controls-work/66347#66347 .  Of course, the paraglider doesn't actually have dihedral like your model airplane does, but it acts like it, due to the "pendulum effect" ( https://aviation.stackexchange.com/questions/53437/does-pendulum-effect-apply-to-hang-gliders-or-any-aircraft/56548#56548 )  Btw, the Gossamer Albatross ( https://en.wikipedia.org/wiki/MacCready_Gossamer_Albatross ) also used "wrong-way" ailerons.

Most likely the adverse yaw effect (due to the induced drag of the increased lift on the down-aileron side) is causing the wing to yaw the opposite direction from the intended roll, and the yaw causes the dihedral induced roll (proverse to the yaw) to override the aileron input.
This situation is very commonly seen with very slow flying model aircraft -- indoor Peanut scale, for instance, or Penny Plane models, will often be set to turn left by putting a relatively tiny tab under the left wing, where you'd expect the lift to cause a roll to the right.
This opposite turn/bank effect predominates in very slow flight because the small differences in lift due to low deflections or small tabs are quite minor at low speed, while drag changes (especially with the relatively long moment arm of a drag tab on the outer section of the wing) are larger relative to other forces in play.
The general rule in trimming free flight models is that roll effects (from ailerons or tabs adding or subtracting life on one wing) will predominate at high speeds, while yaw effects (primarily produced by drag tab, as fin/rudder deflection is prone to produce a spiral dive) will predominate in slower flight.  And extreme case is hand launch gliders, in which a single small tab under the left wing will cause the model to climb to the right (at the high speed -- up to 40 m/s or higher with a well-trained flier) due to the lift effects, but then glide to the left (at speeds as low as 4-5 m/s) due to drag effect of the same tab.

Great answer! But can you elaborate why this effect is more common on slow flying model aircraft? In addition, can it be solved by having a larger vertical stab?

In some aircraft, such as the Canadair CP-107 Argus, the control yoke is not actually connected to the ailerons. Rather, they are connected to servo tabs, which are basically small ailerons attached to the rear of the actual ailerons (not to be confused with trim tabs, which look exactly the same but are controlled differently). Turning the yoke left causes the left servo tab to angle down, which deflects the actual aileron up. The aileron deflects the air stream upward, pushing the left wing down. The opposite happens on the right aileron and tab, raising that wing.
This effect can also occur unintentionally. For example, the Boeing B-47 Stratojet couldn't fly faster than 425 knots; above that speed, the ailerons would twist the wings so much that the airplane would roll in the opposite direction from what the pilot commanded.
I think it's likely that you're experiencing this. It's possible that the upward-turned aileron is twisting the whole wing downward enough that the plane rolls in the opposite direction from what you wanted. If that's the case, your options are to either stiffen the wings somehow, or just accept that your ailerons are going to work in the opposite way than you think they should.

can you elaborate why this (adverse yaw) is more common on slow flying aircraft

It may be a very good illustration of how Reynolds number can affect Lift to Drag ratios of airfoils and how Newtonian deflection of air by the bottom wing (downwash) helps drive low pressure creation (Coanda) on the upper wing only when velocity is sufficient.

Reynolds Number = wing chord m x Velocity m/s ÷ (1.46 x 10$^-5$)

Model aircraft can be faithfully scaled from full size because their density, or wing loading, is much lower.  But, as @Zeiss Ikon pointed out, at lower speeds drag effect of a trim tab will predominate.  This is consistent with L/D data presented at here at various Reynolds numbers.  Small, slow models tend to be around 20,000, whereas full scale aircraft in the millions.

can it be solved with a larger vertical stabilizer?

This is exactly why rudder is used to counter-act adverse yaw.  You make you vertical stabilizer "larger" by increasing its "sideways" coefficient of lift when you use coordinating rudder.
For a your free flight model, you can take advantage of the slow fight drag effect by not using ailerons.  Just make a little rudder on the side of the wing tip fold you desire to turn into.
This is nothing radical at all.  Using rudder yaw lets the dihedral roll the plane.  This technique was common in 2 channel R/C aircraft years ago.

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text:
Where can I find old (historical) FIR map?
I'm doing a research with FIR Ho Chi Minh (formerly named FIR Saigon).
I've read a document which said:

During the Fall of Saigon, ICAO, in 28th of April 1975, had divided FIR Saigon into 3 AOR: Bangkok, Singapore and Hongkong, then they gave these AOR to the corresponded FIR.
In the 7th of December, 1994, ICAO sent AOR Bangkok and AOR Singapore back to FIR Ho-Chi-Minh.
In the 1st of November, 2001, ICAO gave part of AOR Hongkong to FIR Ho-Chi-Minh, and created AOR Sanya from the remained part of AOR Hongkong.
In the 8th of June, 2006, ICAO changed AOR Sanya to FIR Sanya

I managed to search those old FIR maps in the internet but no luck for me.
Hence, I would like to find out all historical FIR maps to make a comparison.
If it is impossible to find all FIR maps, old FIR maps of South East Asia FIR is greatly appreciated.

I hate to say this, but I think your only help might be an old pilot who used to fly in those days. If you live inside one of the regions, you may try your luck at the local library looking for publications of the aviation authority dated back to those years.

@kevin I really hate it if it is the truth.

In the continuation of @kevin comment: You may also try the national library, if there's one, which registers any publication for research. You could look for ATC training books (such library would be the Library of Congress in the US, the National Library in Viêt Nam).

The best I can find is a ATC radar screen used in a dated report (appears to be a report by the Hong Kong Civil Aviation Department in 2000). It shows the FIR regions and waypoints of near Hong Kong, Hainan island and Vietnam:

Here is a dated enroute chart of Hong Kong in 1996. I'm not sure if the waypoint names will be useful for your further search:

How I end up with these: for the first one I used keyword "Sanya AOR". Given the dates you stated in the question, Kai Tak airport was still operational during that time. So I searched for charts of Kai Tak. A full set of charts of the airport would contain an "enroute chart" which lists waypoints. Search engine is Bing.

I have just found this document http://www.icao.int/APAC/Meetings/2011_FIT_SEA11_and_SEACG18/SEACG18-WP10.pdf It seems like that it used the old map dated back to 2000 or before. Then, I concluded that in the shape with SQ0866 was belonged to FIR Hongkong, now part of it belonged to Hongkong and remain part belonged to Sanya. The shape with a lot of islands was belonged to FIR Ho-Chi-Minh, now part of it belonged to Sanya, remaining part belonged to FIR Ho-Chi-Minh.

1 vote for you  but I will leave this as unanswered. So, we can continue on this find.

This is a photo from the 1954-1955 Hong Kong Civil Aviation Department Annual Report
Maybe too late to post, but I just want to share it on the internet as a record.

Welcome to Aviation.stackexchange.com! Nice find!

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text:
What is the minimum engine hp needed to fly a light aircraft with an adult

And also the wing size, propeller sizer, body size, ruder, elevator needed.
I might sound stupid; I am a beginner and I just want to these basis.

Not stupid, but way too broad of a question. You are basically asking the whole set of design priciples for a small acft.

The answers to this question may be of help:  https://aviation.stackexchange.com/questions/45160/can-an-ultralight-aircraft-fly-with-a-18hp-engine/45161#45161

You might want to rephrase the question to eliminate things like gliders and balloons.  Something like "What's the minimum power needed for a plane to maintain altitude in still air?"

@ymb1 Human powered aircraft have wings, propellers, rudders, elevators, etc, as in the OP's question, but no engine.  I don't see anything "tongue in cheek" in pointing out why the question was too vague to answer.

Gliders fly without any engine at all, therefore, I would say the minimum horse power required is 0.

"Gliders fly without any engine at all": I guess that's a simplification. Gliders need engines and fuel to become airborne, even if there are particular cases: One time flight from a hill, winch rotated by wind, etc.

It is perfectly possible for a glider to take off from a hill top with no mechanical engine or winch power, climb using the lift from the wind blowing over the hill, and land back on the same hill top for another flight.

Hydrogen/Helium balloons fly without any engine at all, therefore, I would say the minimum horse power required is 0.


text:
"Left overspeed" on MD-11
The MD-11 has an overspeed and a left overspeed call-out alarms. This is different from the modern planes counterparts, in which a tick-tick-tick sound is used instead.
What does left overspeed even mean and why is there no right overspeed?

I heard (now with the fabulous answer I should say misheard) it in https://invidious.protokolla.fi/watch?v=TK5K9pJo67w.

I think you misheard that: it doesn't say "left overspeed", but "slat overspeed", when the maximum speed with slats extended is exceeded.
You can hear the call out e.g. in this YouTube video. The MD-11 FCOM doesn't explicitly list the call outs, but it explains that both overspeed conditions result in an aural alarm:

Overspeed Warnings
The CAWS will provide an aural warning tone when an overspeed condition is
detected by either Central Air Data Computer (CADC). The CAWS will also
provide an aural warning whenever the aircraft exceeds the maximum speed with
the slats extended.

(McDonnell Douglas MD-11 FCOM - Warning and Alerting - Description and Operation)
The "slat overspeed" is however explicitly mentioned in the final accident report of China Eastern flight 583:

The captain [...] observed the white "SLAT" light with a down arrow illuminate on
the PFD [...] and, at the same time, the "slat overspeed" warning chime
sounded.

(NTSB Aircraft Accident Report - China Eastern flight 583)
By the way, the "tick-tick-tick sound" you describe is created by the clacker, which is used at least since the 1960s (so I wouldn't call it the modern counterpart). The MD-11 also has a clacker:

The clacker will sound when airspeed exceeds 280 knots and
the slats are extended. [...]
Overspeed
AURAL - clacker.

Logic - airspeed above Vmo/Vmo plus 4 KTS or above 280 KTS with
slats extended.
Inhibit - takeoff (80 KTS to 400’ RA) and landing (100’ RA to 80 KTS).

VISUAL - red and white bar on airspeed tape on PFD.

Logic - airspeed above Vmo/Vmo plus 4 KTS.
Inhibit - none.

(McDonnell Douglas MD-11 FCOM - Warning and Alerting - Description and Operation)


text:
Any general aviation terminals have jet bridges?
Has anyone seen a FBO or general aviation terminal with a loading bridge for passengers? I remember flying into PHL on a commercial flight landing at Terminal F and they had ground level loading bridges, so they do exist, just not sure if they use them for private aircraft or charter airlines.

Near as I know, the answer is no. But who knows. It’ll be interesting to see what people come up with in the comments.

I have on another forum website  made aware of at least two in the United States, seems they are rare, however do exist. One is at Topeka Regional Airport the other at Oakland International (PTK) in Waterford, MI.

What is a "ground level loading bridge"?  By definition a bridge would normally span two points that are above ground level...

Philadelphia International has them in Terminal F you can depart a regional jet or other small commercial airliners and the terminal end of the bridge is at ground level connected to the terminal.


text:
Is there a specific name for an airport gate at ground level?
At a two level airport most gates are located on the upper level with loading bridges or jetways. Is there a specific name for gates located on the lower level (ground) for like use of turbo prop airliners or small jets that do not use a jetway?

Cargo/luggage gate?

The parking spot of the aircraft on the ramp is commonly called a "stand".
The exit to the ramp (either directly to the aircraft via a jetbridge or to say a bus stop) is typically called a gate.
That's internationally accepted terminology, but I can't guarantee that there aren't airports or countries where other words are used (especially if languages other than English are the norm there, obviously).


text:
Is there a minimum distance a building must be from a taxiway or runway?
Is there a minimum distance a building on the actual airport property must be from a taxiway or a runway? Two examples of a building would be the terminal and concourses or any hangers for example.

There is the concept of a safety area (runway safety area or taxiway safety area) in which there should be absolutely nothing taller than a blade of grass, in order to protect aircraft which might depart the pavement. In the united-states a runway which is intended for use by air carriers will generally have a safety area defined as 250' either side of the centerline (or sometimes 250' either side of the runway edge) and 1000' from the ends of the runway, although this is not always the case.
Of course having absolutely nothing in the safety area is an unachievable goal, because there is certain infrastructure which must be present: Pavement edge lights, glide slope antennas, taxiway signs, etc. These features are often designed with special frangible bases so they shear away when they are hit and ideally do not damage the aircraft which hit them.
In the final analysis, the minimum distance a building must be from a runway/taxiway depends on the wingspan of the aircraft which are going to use that runway/taxiway. It is common to have certain taxiways be restricted to only aircraft under a certain wingspan; as a random example, here is one such restriction which applies at Atlanta-Hartsfield:

Acft with wingspan greater than 171 ́ are rstd from using Twy V.

More information and further sources can be found at this answer regarding aircraft-to-aircraft separation on taxiways/runways.

There are rules for setting glideslope descent path slopes to clear buildings in the approach path by a certain margin of feet, but sometimes they cannot be followed. For example, some years ago the bottom of the glideslope path tolerance stack intersected several tall buildings in downtown San Diego that were in the approach path. I do not know if this issue was ever resolved but since I no longer fly into and out of San Diego on business anymore, I have stopped worrying about it.


text:
Can an N registered aircraft operate scheduled service from USA to/from a Category 2 country?
Am looking at economics of a scheduled service between Honolulu and Tarawa but need an N registered aircraft to do it.

Can you fill us in more on what a "Category 2" country is?

This one is probably more of a question pertaining to policies of the US Dept of State than Aviation.

Possibly IASA categories (compliance with ICAO safety standards). Need to be clarified. A Category 2 country is one where an operator of this country cannot open a new service/codeshare with the USA. Example and return.

I don't see what's unclear about this question. It's very specific. Vote to reopen

@TomMcW: This is about which category the OP is talking about. The OP can clarify easily.


text:
What to do to maintain my Spanish ULM (GA) gyroplane licence valid in the USA when moving there?
I have an ultralight gyroplane (GA) Spanish license. What sort of conversion or validation process do I need to follow to be able to continue flying after moving to the USA?

I suggest you should join the Rotary Wing Forum and ask there... Several members are gyro CFIs in the USA...

Do you mean a) you want to keep your Spanish license valid while living in the US, or b) you want to use your Spanish license to fly in the US? I have no idea about (a) because it depends on EASA/Spanish regulations, but for (b) you can check this question

@Pondlife: It could be my edit which is ambiguous. "after moving to the USA" means when I'll be in the US, will I be authorized to fly with my Spanish license, if not what should I do?

@mins Ah, I didn't look at the edit history. In that case I'd say it's a dupe of the other question I linked in my comment.

Possible duplicate of I have a European EASA license - what do I need to do to be allowed to fly in the US?

@Pondlife: I wonder if ULM (is that the correct term in the US?) licenses are managed the same way, at EASA level, (typically in France I understand there is no examiner, only an instructor, and no medical exam with an accredited doctor, only a GP paper).

In Spain, in order to obtain a ULM gyro license, (I have one...) you need to pass an official examination and also a medical type II.

@mins Good point! I don't know if a ULM license is enough to get an FAA foreign-based license. I gave an answer that covers both cases (I think). VtC retracted.

As a caveat here, I know nothing about gyroplanes. But based on the US regulations it looks like there are a few different possibilities.
If your ULM license is equivalent to an ICAO private license then you could get an FAA foreign-based private license as described in this question. I believe you would get category rotorcraft and class gyroplane (see 14 CFR 61.5) but I'm not completely sure.
If your ULM license is not equivalent to an ICAO private license then it depends on the type of gyroplane you want to fly. If it's considered an ultralight then you don't need any license at all. If it's an LSA then you would need a sport or recreational pilot license. If it's a 'regular' gyroplane, you would need a private license.
If you do need to get an FAA license (sport, recreational or private) you should be able to use time you logged in Spain to count towards it.

In Spain, an ultralight gyro is a machine with a MTOW of 450 kg. A few kilos more in some European jurisdictions.


text:
How is the moment due to pressure distribution calculated?
Consider the airfoil shown, with a co-ordinate system set up from the leading edge $O$:

I want to find the moment of force about point $O$ due to pressure on an infinitesimal piece of the airfoil at point Q.
A text book I'm referring to(Fundamentals of Aerodynamics by John D Anderson) says that the moment is:
$$ dM= (p dS) cos \theta ~ x_Q $$ (where $x_Q$ is the x co-ordinate of Q)
Is this expression an approximation that assumes thickness of the airfoil to be negligible compared to the chord length?
Because, the moment should be length $OQ$ multiplied by component of $pdS$ perpendicular to $ \vec{OQ}$ ... or have I made a mistake with the physics?

Yes, you seem obviously right, the correct way is "pressure component perpendicular to surface" times "distance from pivot axis".

If you calculate "component of pdS perpendicular to OQ" you get
$$ dM= (p dS) (cos \theta ~ x_Q + sin \theta ~ y_Q) $$
The pressure times the surface (gives you a force), splited in the two perpendicular forces(along axis) and applied at the $x_Q$ and $y_Q$ distances. Set $y_Q$ to 0 (negligible thickness) and you get the book formula.

Also consider that for a typical wing, $\sin\theta$ will be smaller than $\cos\theta$ except near the leading edge.


text:
It is possible to feel a difference between helicopters with clockwise direction rotor and counterclockwise rotor?
From the perspective of a pilot, is there a difference when flying a helicopter with a clockwise turning main rotor vs a counter clockwise turning main rotor?
Would a pilot notice if they flew the exact same helicopter except with an opposite rotation (and obviously all the corresponding mechanics mirrored.)

Yes, the pilot would certainly notice the difference.
When the engine applies clockwise torque to the main rotor, the body of the helicopter experiences counterclockwise torque. When the pilot increases collective to increase the amount of lift the main rotor produces, the engine will need to apply more torque to overcome the rotor's increase in drag. Therefore the pilot would have to apply right pedal to prevent the torque from turning the nose of the helicopter left.
If the rotor turned counterclockwise instead, these directions would be inverted. So if the pilot was flying the helicopter with the assumption that the main rotor turns in the opposite direction that it really does, he would tend to apply the wrong pedal and the helicopter would start yawing.

I've flown both.  Apart from the pedal reversal and looking at the blades, there are no physical cues that I am aware of.  As an aside, there are some circumstances in which the pedal reversal can be potentially dangerous.  For example, in entry to auto-rotation, lever down, stick back, right pedal in.  Except in a clockwise rotating machine when it needs to be left pedal in. Getting the wrong pedal can quickly lead to an "unusual attitude" which needs rapid correction to avoid a loss of control.  A pilot changing from one to other an impulsively reacting with muscle memory might get it wrong.


text:
Why Boeing 737 main landing gear wells have no doors?
My question is about the Boeing 737 main landing gears:
When the landing gears are up you can see a landing gear door to open in most planes and then it closes. But for Boeing 737 main landing gear are not behind well doors at any time of the flight.
Why are main landing gear wells opened during in flight?

Related if not duplicate

similar but not answeres to my question

The question is more general than this, but the answere is good.

There's This one too

To keep costs down. The extra friction from no gear doors is more than made up from the weight savings.

Arguably: the proportions of the aircraft. The engines are tucked up close under the wing, permitting short landing gear. Retracting the wheels into the body of the aircraft (instead of the wing) allows the engines to be placed closer to the fuselage (better engine-out handling). But, the body is quite narrow, so the wheels in retracted position end up quite close together, leaving little to no room for doors. The wheel wells have "brushes" which help smooth the gap between the aircraft underside and exposed wheels, minimizing the drag penalty.


text:
Is it possible to get the QNH value in Austria using a web service?
I got a altimeter sensor which can be connected to a computer and can be adjusted by the QNH!
I need the QNH for Austria, I figured out that the current QNH of the airports are streamed via radio.
Are QNH provided as text format or even better web service, so I can fetch mine automatically for transparent altimeter setting?

The current QNH at an airport is included in METARs so you can grab it form there. There are a few online services to retrieve the METAR automatically, such as this one (using Vienna airport as an example).
The latest METAR when I wrote this answer was:
LOWW 281050Z 14010KT 9999 FEW040 SCT065 BKN300 04/M03 Q1012 NOSIG

which shows a QNH of 1012.
Note that depending on the country the format may vary slightly, but in Austria (and European countries) you should always find a Qxxx value in the report.


text:
Was the Wright Brothers' 1902 machine a working glider or just a kite?
Was the Wright Brothers' 1902 machine a working glider or just a kite?

I spent the last days reading the letters and articles of Amos I. Root, the man who claimed he had seen Wilbur Wright flying his plane in a circuit on September 20, 1904.
I had already been aware that the 1903-1905 powered flights of the Wright brothers could be a fraud but I was convinced, before reading the above mentioned book, that the 1902 machine was a true glider that could be flown in a stable manner for 600 feet.
From what I have found on the internet (see the two attached videos) it appears that the 1902 glider could be more a kite. I simply do not find videos with this apparatus in free flight for distances like 100-200 meters or even shorter.
Question: Have somebody built a replica, of the 1902 apparatus, that flew without being towed and kept stable by people on the ground?

The letters of Amos Root to the Wright brothers and his articles about them.
Click to download the book.

A replica of the 1902 Wright glider.
Click for the video.

A replica of the 1896 Chanute Herring glider.
Click for the video.
The 1896 Chanute-Herring machine is a real glider, as ca be see from the video. It does not fly long distances but its stability is remarkable.

The Wright brothers are first by contract anyway. This makes things a lot more simple.

It worked, but it did not have good performance, so they flew it as a kite instead.


text:
How to calculate the takeoff speed for a hypothetical aircraft?
Given some basic information such as:

aircraft weight
wing load (including wingspan, and basically the whole wing configuration)
airfoil profile
coefficient of lift
angle of attack

Is it possible to get an estimation of the minimum takeoff speed?
And we are not speaking here about the conventional takeoff (until aircraft reaches 15m altitude), but the minimum speed relative to incoming air until the lift force overcomes the weight of the aircraft.
My first thought about this was to use this two formulas:
$L = \frac{1}{2} \rho v^2 A C_L$ and $ v^2 = \frac{2g W_S}{\rho C_L} $
where:
$C_L$ = coefficient of lift (this, of course would depend on airfoil and angle of attack)
$W_S$ = Wing loading
But as I'm just scratching the surface of this field, I am unsure if my logic is solid and I'm here to ask for help.

Knowing how you intend to use the information once you’ve found it will help decide how good your estimation needs to be.

With the parameters given, all you can do is to calculate the minimum airspeed. Adding available thrust would help to determine whether the plane would actually be able to climb and now ground effect will lower this speed, possibly below minimum sustained flight speed.

Excluding safety factor of a little excess airspeed before rotation and excess thrust/angle of climb considerations:

Weight = Lift = 1/2×rho×v$^2$×Area×Clift and Ws = Weight/Area

Multiplying W by g would convert your weight force into Newtons, otherwise your two formulas are interchangeable.
For these calculations, special attention to the AoA part of the Coefficient of Lift would be important to establish a safety margain.  Because Lift is proportional to v$^2$, a little extra airspeed can be very useful in reducing drag and improving climb performance.

Weight and lift are both forces. No need to 'multiply by g'...

Yep. Weight=mass X g.


text:
runway-restricted airports?
A video about the improvements on the A330 Neo says that its new flaps settings make it better at runway-restricted airports.  What does that mean?

The "runway restriction" mentioned in the video means that the runway length may be too short for some aeroplanes altogether or it may restrict the maximum takeoff weight for certain aircraft, since the heavier the aircraft is, the more lift it requires to take off.
As described in the video, one major factor in takeoff performance is the flap setting. Flaps increase the lift provided by the wing, enabling takeoff at shorter distance. The downside of higher flap settings is increased drag.
Due to the nature of lift and drag equations, there is an optimum flap angle for any given weight and runway length combination. Unfortunately the flap settings in aircraft are discrete: there is a limited number of settings to select from, meaning there may be conditions in which the lower setting is too low (producing too little lift), and the next one is too high (producing too much drag).
The A330 Neo mitigates this problem by providing additional flap settings to "fill the gaps", enabling better optimized takeoff performance. I made a screen capture of the video showing the additional settings place in between the original ones, with green and red dots I added. The graph is interpreted such that the area below the bold black line is usable, the area above the line is impossible to achieve: if the weight and runway combination plots over the black line, the aeroplane will overrun the runway on takeoff.

From this graph you can see that the areas marked with the red dots were not achievable before with runway lengths marked with respective green dots on the horizontal axis. Either the plane was too heavy, or the runway was too short. With new intermediate flap settings extra lift is available without critically more drag.


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Is this flight GPS data intentionally manipulated?

Some flat Earth guy is trying to convince me that flight data is manipulated with and that planes travel faster in the Southern Hemisphere.
Now this is obviously not true, in the video speeds of over 800mph are recorded in some shady screenshots, most jet streams can't get you that fast, much less many flights doing this at the same time.
It's either the screenshots are faked, or that there is some explanation as to the discrepancy between the two numbers.
If anyone can clarify this for me I would truly appreciate it.

I think you're just wasting your time: you want to convince someone who thinks that "data is manipulated", using... data!

Arguing with an idiot is like wrestling with a pig: You both end up in the mud, but the pig enjoys it.

@ROIMaison  Can I borrow this?

You're probably right, I just wanted to know how I can show that it is manipulated or seriously misunderstood. But just making sure, the data in the video is NOT real?

@sophit of course! [just like I borrowed it ;) ]

A flat-earther faking screenshots?  Who would have thought it?

Have been bored about 2 minutes in, but he clearly states at the beginning that whatever he is showing you is a simulation. And that… it’s a globe. You can actually see the curvature on his simulation (!), he seems to believe in GPS (!!!), he doesn’t understand why we don’t receive ADS-B data over oceans… Yawn.

"Southern hemisphere": read the last 5 characters. Also GPS requires a spherical Earth. You can see position of satellites and how to calculate your position: if would be very difficult to build an alternate view -- In any case, everything can be true, Allegory of Plato's cave tell us so, but you can decide: you can live in a library discussing philosophy ad infinitum (and no conclusion) or just get a life (you can still discuss philosophy, but ...)

Uh wow. I managed to muster the courage to watch (mostly try to listen) the whole drivel video.
What you have to remember is that flat earthers fall into two categories:

Those who are just plain stoopid™
Those who know perfectly well that the Earth is not flat but just continue with the charade. Don't know if they do that just to take advantage of the plain stoopid™ people, if it's just for fun (hey, it's cool to be part of a "Society") or whatever other reason.

I hope for them that the majority are in the second category, but hey, whatever. You can make all the rational arguments you want, the first ones will just ignore them because they beleeve™, the second ones will ignore them because it's no fun. The good thing is that at least it does not kill millions of people like some beliefs do, just themselves (striking example of a flat earther who was in both categories at the same time: he didn't believe it, pretended to in order to raise money from the plain stoopid™, but was himself stoopid™ enough to try to send himself up in the air in a homemade rocket...).
But let's get back to the claims in that video.
Apparently the whole story is that a french guy took 2 weeks worth of FlightRadar24 data he just doesn't understand and played with it and found all sorts of... Well, nothing.

The first part of the video is some kind of simulator doing a replay of a bunch of flights (accelerated many times). The simulator actually shows a globe, with visible curvature. Not sure sure what the point is here.

Then the second part of the video shows a few southern hemisphere flights, and alleges that the ground speed given by FR24 does not match his own calculation of what it should be (by about 300 km/h, plus in one direction, minus in the other). The examples are LAN800/801 (Sydney-Auckland-Santiago and back) and QF27/28 (Sydney-Santiago and back).
For instance he says that QF27 (flying West-East) was at some point shown by FR24 as flying with a ground speed of 557 knots (1032 km/h) while his calculations tell him the GPS data shows that the actual speed was 1319 km/h. Another example is LAN801 (flying East-West) shown at 458 knots (848 km/h) where the GPS data supposedly yields 548 km/h. So obvioosly™ the GPS data must be wrong/faked.
I took the JSON data for a flight from FR24 and did the computations myself. While there are differences between the ground speed reported by FR24 and what you get when you compute the speed from the last two positions:

A lot of it can be explained by the fact that the timestamp (in the JSON at least) has a granularity of a full second. When records can be spaced anywhere down to 3 seconds apart, that makes a huge difference: 581 meters in 2 seconds is 1047 km/h. The same distance over 3 seconds is only 616 km/h!

I'm not sure if the timestamp is when the data was received by FR24 or by whatever receiver got the ADS-B message first, or when the aircraft sent it. Given the combination of ground based and satellite-based data, this can explain a lot.

Some discrepancies may be due to the switch from one source to another

Using the per-record speed, you would see it do things like 374 - 262 - 540 - 268 - 473 km/h etc, spaced 2 to 4 seconds apart. Obviously the ground speed does not change that much in such short periods of time! It's just a result of the timestamp rounding.

The speed data reported by FR24 is probably just an sliding average over a slightly longer period to smooth things out

Most importantly: while there can be a few differences over 300 km/h on individual records (mostly when the interval is very short, around 2-4 seconds, or when the interval changes significantly, which is probably the sign of a switch from one data source to another), they cancel each other out, and in the end, the average difference is only 2.5 km/h on the flight I looked at.

So no, there's nothing suspicioos™ here.

They exclaim at the fact that ooooh, over the ocean where it's more difficult to compare whatever FR24/GPS data and reality (you can't have a bunch of flat Earthers checking that the plane is or isn't where the "Globers" pretend it is), there is a lot of data missing. Duh. Maybe trying reading the data sources page of FR24 and understand that there are lots of places which do not have coverage?

They marvel at the fact that planes over the North Atlantic suspicioosly™ fly very neat routes, lots of straight segments, on a number of nicely equally spaced routes, and this is all way too clean to be true when compared to the mess over the US or Europe. Ooooooh they discovered the North Atlantic Tracks.

Ensues an explanation for the fact that there is very little data over the North Pole, but it may just be because it's difficult to manipulate lat, long data near the poles (probably the case if you didn't listen in school), but it may also be because "they" want to hide something. Sure, sure. Or it could just be because of lack of coverage as above, combined with the fact that the current avoidance of the Russian airspace makes most polar routes unusable at the moment.

Small diversion alleging that there are no pictures showing the North or South Poles, it's either always masked or CGI. Yeah yeah.

Then some discussion about suspicioos™ curved routes (as visible on their very funny flat earth azimutal equidistant projection), which are probably the proof of the existence of GPS towers (!). More like great circle routes...

Then they find it highly suspicious that there are very few flights inside the Southern Hemisphere (the video does not show the images they're looking at at that point, but I supposed they mean transatlantic and transpacific routes). Well, indeed, there are very few because the market for them is very limited. Not sure what is suspicious about that.

Why did you do this to yourself? :p

@Chris  Very good answer though

Really late, but great answer, this is exactly what I was looking for. That flat earther has blocked me already but it's good to have this information in case anyone else brings it up. Thanks a ton, you can rest now

Screenshots are easily faked.
I would describe arguing with a flat-earther as wrestling with a rubber octopus. There's nothing you can grab onto, and unlike you the octopus always has an extra arm.
Airspeed numbers are only as accurate as the GPS readings they are based on and the data transmission quality, and glitched data will yield false numbers. Fact-deniers are expert at zeroing in on things like that and disabusing them of such cherry-picking is a fruitless enterprise.

Fair enough haha. I really shouldn't let them get to my head.

Even in statistical science, there's a reason why a p-value is used. If you take enough measurements, you'll eventually get false positives.


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How are the wings of a mono- bi- or triplane referred to with regard to position?
Apologies if this is an elementary question. If I look at a diagram for parts of a plane, they don't distinguish verbally between left/right. If I try Googling for, say, "right wing" or "left wing", well you can guess the result!
Suppose I wish to identify a feature, say, the topmost left-side wing of a triplane, how do I do it?

Why isn't "right upper" or "left lower" adequately descriptive?

@Ralph - maybe it is. That's what  I wasn't sure of. I wanted to comment on a photo and didn't know the correct terminology. I'm used to sailing - boats don't have a left and right, they have a port and starboard. Road vehicles have nearside and offside (driver's side). I'm assuming from your comment that planes have left and right sides. Does this also apply to the lights they must display when flying at night? Left and right nav lights?

Okay, I see where you're coming from.  Answer provided -- see if this gives you what you're after.

@chasly  Due to sensible countries having the drivers seat on the right-hand side, 'left' and 'right' are more sensible than nearside and offside in many conversations about road vehicles.

@chasly-supportsMonica If you describe something as being on "the left side of the boat", everybody will know what you're talking about. Boat people aren't dumb, just overly pedantic about vocabulary.

@Sneftel - I don't think you have done any serious sailing. There are very good safety reasons for using port and starboard. One very basic one is if your small vessel is about to be run down by a large one. On the radio you don't want to get into conversations such as, "Do you mean your left as you face me or do you mean my left as I'm facing you?"

@chasly-supportsMonica The same confusion can occur even in aircraft written documentation. Even a phrase like "the left side when looking towards the front of the plane" is ambiguous: does it mean "when you are sitting in the cockpit looking forwards", or "when you are standing on the ground in front of the plane looking backwards"?

@chasly-supportsMonica Yes, I know the reasons. My point stands.

@You may stand by your point but your point doesn't stand up to scrutiny IMHO. But let us cease this. It is off-topic.

@Sneftel Even people who can't tell left from right can learn  that the port side is the one with the red navigation light. If they don't know the difference between port and vinho verde, they shouldn't be allowed anywhere near a boat ;)

@alephzero - This confusion about who is facing where, was a major reason for my asking the question. In the photo I provided, my left is not the same as the pilot's left. That was what would concern me, were I to refer to the "left" wing when describing the photo.

@chasly-supportsMonica: "I don't think you have done any serious sailing." - as someone else who hasn't done any serious sailing, your comment now leaves me wondering why a conversation like "Do you mean your port side or do you mean my port side?" would be preferrable in any way.

@ O. R. Mapper -  The reason is that, on a ship, left and right have different meanings than port and starboard. L and R refer to a person and P and S refer to the ship. For example, the order: "Move to port!" is different from "Move to the left!" There are various articles online. Quote: "Port and starboard unambiguously refer to the left and right side of the vessel, not the observer. That is, the port side of the vessel always refers to the same portion of the vessel's structure, and does not depend on which way the observer is facing." https://en.wikipedia.org/wiki/Port_and_starboard

@O. R. Mapper - P.S. "Move to port!" is unambiguous. However, if I give the order, "Move left!" then the crew member is justified in asking "My left or your left?"  Why? Because people walk around on ships. They can be facing in any direction when the order is given.  Incidentally, this leads me to wonder about rear gunners in aircraft and how they called directions to the pilot and vice-versa.

@chasly-supportsMonica, probably by the clock face analogy: https://en.wikipedia.org/wiki/Clock_position the rear gunner would face six o'clock.

@ilkkachu  - That sounds very convincing. Of course, in the air there are three dimensions. I wonder how they cope with that.

@chasly-supportsMonica  Oddly enough, when we had an observer with a plexiglass bubble in the C-130 to scan for airborne threats, the clock positions were grease-penciled around, starting with "R1" thru "R5", 6, and then "L7" thru "L11". So the observer's callout (mainly to the pilot) would be a threat at "right 3 oclock high" or "left 8 oclock low". The priority was clear communication to the guy with the controls, and getting him the left/right then clock position then high/low/level  was what was found to work best. HE was always facing front, so there, "left/right" worked fine. Go figure!

While boats use port & starboard, aircraft (at least in the U.S.) generally don't.  "Left" and "Right" work well for most things; when talking with flight attendants (on a large aircraft), "captain's side" and "first officer's side" serve the same purpose as "port" and "starboard" (i.e. the port or captain's side is the same side of the vehicle, regardless of whether it's on an individual's left or right at the moment).  For maintenance purposes, the engines and certain other left/right-side components are referred to as the #1 and #2 (and #3 and #4 if you have them), and when talking with a pushback crew (who are in front of the airplane facing it -- so their "left/right" is opposite that of the pilots) it's common to refer to "the #1 side" (i.e. captain's) or "the #2 side" (i.e. F/O's).  When we would back up the C-130, the loadmaster on the cargo ramp looking behind us would direct "turn toward #1" or "turn toward #4", which worked out nicely.
But, I don't think I've ever heard of wings referred to as #1 & #2, or really as anything other than left & right.  (Those who've flown on aircraft carriers may report a different experience while at sea, I've not done that.) I'd say that the most general case would be to refer to a left/right wing, or on a biplane left upper, right lower, etc, and in a triplane, I'd have to assume left middle (or, perhaps less likely, left center) wing.
The Nav lights are generally referred to as left or right, at least in my carrier's operation.  You could refer to them as "the red nav light" or "the green nav light" but I don't think that's particularly common.
Various different organizations will have their specific conventions, but as a general case, plain (or, "plane") English works well & is a good place to start until the preferred local terminology is introduced.

Thanks. I'll digest that for a while to see if your answer raises any extra queries on my part. For the moment though it seems pretty comprehensive.

When I was in the Air Force, the official position was that almost everything was numbered, left to right. This nomenclature was routinely used for engines, but even though if officially applied to wings as well, I don't recall hearing anybody ever actually use it for them.

@JerryCoffin Yeah, anybody who mentions "the #2 wing" probably gets a sideways glance most of the time.  "Left engine" and "Right engine" would be easy enough, but "left inboard" and "right outboard" start to get cumbersome, so #2 and #4 are easier there.  (Might be fun to try to describe the different motors on the B-36 without numbering them... but probably not very efficient!)

@Jerry Coffin - That numbering holds for weapons stations as well. F-16, Sta 1-9, left to right. Sta 1 is the left wingtip, Sta 9 is the right wingtip.

Any lateral confusion is dealt with in Ralph J's answer.  The rest is straightforward:
For a biplane or triplane, vertical confusion should be eliminated by the usual upper, middle, lower.

Is there one uppermost wing or two?

This becomes clear in context.  "The wing" without further qualification means the entire primary lifting surface, whether or not it is interrupted by the fuselage (for an airplane, but not for a bird!).  "The left wing" or "the left uppermost wing" means the left half thereof.

Don't overthink it.  It's simple; left top (or upper), mid, and bottom (or lower), and right top (upper), mid, and bottom (lower) are perfectly clear and precise.  On a biplane, just take out the mid, and on a monoplane, it's just left or right.
You can substitute port for left and starboard for right, but if the audience is outside the aviation/boating world, most people won't know what you're talking about and will have to look it up (and some pilots will also have forgotten and have to check which is which), so the majority of the time left and right is used.


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Why new jet aircraft have wider, larger cockpit windshield/windscreen?
If you compare aircraft in the same category Boeing 737 with newer Airbus 320 and more recently Comac C919 or Irkut MC-21, it is striking to observe the changes in the cockpit windscreen design.
The trend seems clearly to be wider, larger windscreens. What are the reasons for that?

Because we're getting better and better at allowing pilots to see where they are going and what's going on around their aircraft?

The area of the windscreen is limited by the structural strength of the materials. The windscreen must withstand the difference between cabin pressure and outside air pressure during cruise. In addition, it must also survive impacts from birds and hail to a certain degree.
As material engineering advanced, we can produce larger windows and windscreen. For example, even though the Boeing 787 has a stronger pressure differential (6,000 feet cabin altitude vs 8,000 feet in traditional airliners), the passenger windows on the 787 are larger than previous productions.

Undoubtedly, your answer is true as far as it goes.  Alas it presumes that bigger windows are inherently a good thing that was long desired but unfeasible for decades.  The OP's question, IMHO, is at least partially questioning why is bigger better?  Certainly I have cursed the sun during IFR which often makes it hard to see the instruments; smaller windows would be good thing then, or at least visors and/or window shades.

I've never met a pilot who wished he had less visibility outside the cockpit. Shades work pretty well to block the sun when needed.

do bigger cockpit windscreen, and more advanced materials allow for better aerodynamics? Or is it only a matter of vision for pilots?


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What is the history of Concorde motto "May Concorde bring people closer" and medal?
I found this image of a medal figuring Concorde and a globe with two contours of continents, before and after Concorde, expressing the new speed of air transport with a motto "May Concorde bring people closer." ("Que Concorde rapproche les hommes").
As I find this material extremely relevant to express the global geography of time-space during the supersonic period, to I would like to know more about it:

Where does this medal and motto come from?
Was it present onboard?
Was it used in other forms of communication?

Another medal with the same motto.

I see Antarctica is still as far away as ever...

That medal is a copy of one that was presented to Queen Elizabeth II by M. Ziegler (S.N.I.A.S) during a state visit by the queen to France in 1972, sometime between 15–19 May. The most likely date would have been 18 May, when she visited a SNIAS helicoper factory and was accompanied by Mr. Ziegler.
It was presented to commemorate the intention to build the 'Concorde' for commercial supersonic flying and currently sits in the Royal Collection Trust. "M. Ziegler" is Monsieur Henri Ziegler, who passed away in 1998 at age 91.
"In 1968, he was appointed to run Sud-Aviation, a leading aircraft manufacturer in the south of France, and charged with reorganizing the badly splintered aircraft industry. Sud-Aviation was later absorbed by the larger Societe Nationale Industrielle Aerospatiale, or Snia, which in 1984, as the core of the French aerospace industry, was renamed Aerospatiale S.A."
That is where the "S.N.I.A.S." comes from, "Société nationale industrielle aérospatiale". The Concorde was built by British Aircraft Corporation (BAC) and Sud Aviation. Mr. Ziegler was instrumental to the partnership, and was seen by some, at the time, as a traitor to France for suggesting it.
I think it is fair to say that this motto was coined by Ziegler for the creation of the medal, likely to express his gratitude for England's role in the partnership, but it is not the official motto of the Concorde.
British Airways' slogan for the Concorde was "Arrive before you leave." I honestly don't remember, nor can I find, a French slogan for the Concorde, but the slogan for Air France is "France is in the air."
It was a lot of fun researching the answer for this.


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How can some stretched derivative airplanes have longer range while most have less?
On the one side A321 neo has almost the same range as the A320 neo (250 NM difference), and a LR version of A321 neo will have an even longer range. The same goes for  the Dassault Falcon 7x and the longer and longer-range Falcon 8x.
On the other side Boeing 737 MAX line shows a clear tendency: the longer the fuselage the shorter the range. The same tendency can be observed on most aircraft types.
I understand that fuel is generally in the wings which keep the same volume on a stretched derivative, but fuselage can accommodate fuel tanks and range can be a crucial point for aircraft. So why don't/can't aircraft manufacturers propose equivalent range stretched aircraft in general, as the A321 neo does?

My guess would be that the stretch is designed to accomplish a particular task. In some cases the task is to go farther, in others it's to carry more over the same (or shorter) range. Each manufacturer designs for the market they believe is emerging, to the niche they see as empty. For example, Boeing has ER & LR versions of the 777 which aren't any longer than the standard range, but have additional fuel tanks and increased MTOM.

Also compare the Falcon 7x and the longer and longer-range Falcon 8x

@CodyP and the infinite range Falcon 9 :p

When aircraft are stretched, they usually just receive extra fuselage plugs on both sides of the wing: wing redesigns are incredibly expensive and take a long time. So the longer aircraft has a higher empty weight, and due to the unchanged wing design the fuel capacity remains the same - this reduces range. The aircraft is fuel limited. Conversely, if fuselage plugs are removed the same amount of fuel can take the aircraft further, as the B707-138 demonstrated, Qantas' first jetliner.

The A321NeoLR fixes the fuel limitation by adding extra fuel tanks in the cargo bays as this article explains, so that the aircraft now becomes weight limited. The extra fuel means that there can be less extra revenue from cargo. The B737-9 cannot follow suit, because it is has a shorter landing gear and has rotation limitations: from this article:

737 MAX9 is not suitable for stretch to an international version, not because the wing is not good enough but because the MAX9 cannot bring the wing to an angle at take-off where it can work efficiently; the landing gear is too short.

The longer fuselage limits the rotation angle before a tailstrike occurs, so max. TO weight has a hard limit that cannot be managed by trading cargo weight for fuel weight. Above photo is from this site, which also contains a table with geometric angle limitations for the different 737 versions: the -9 has a tail strike pitch attitude of 10 deg, and has increased flap deflection of 25 deg to limit lift-off attitude to 6.8 degrees. A small variation in centre of gravity at a high TO weight can cause a tail strike.
Boeing has launched the B737-10 which will address the rotation limit by a redesigned landing gear.

@ymb1 Thx, and the F70 and the B747SP.

Just to comment regarding wings: Boeing 777-300ER is a "stretch" from 777-200 and has larger wing area. Same for MD-11. Same for A321 (despite what wikipedia says A321 seems to have larger wing, + additional winglets also increase the area)

please @koyovis explain the link between "shorter landing gear and has rotation limitations" and the impossibility of "extra fuel tanks in the cargo bay" for the 737, this is unclear to me

@ymb1 - According to other opinions here https://www.quora.com/What-is-the-difference-between-the-Airbus-A320-and-321-aircraft and here http://www.airliners.net/forum/viewtopic.php?f=3&t=548239&p=7670407&hilit=yehudi+a321#p7670407A321 wing has slightly larger area and as you say different flaps. So I wouldn't call it the same wing. It has the same fuel capacity, but has slightly higher lift power due to wing area increase.

@ParadigmPilot the main structure and shape of the wing (profile, spars etc) remains unchanged. Tweaks such as increased flaps and winglets are added as much as possible within the limits of not having to alter the main wing geometry.

@ymb1 Aha, a dropped penny.

@Koyovis  - "…TO weight has a hard limit that cannot be managed by trading cargo weight for fuel weight."
Why not? If you still have a headroom within Maximum Zero Fuel Mass, Max Take Off Mass and got some empty space in the fuel tanks - you can substitute passengers with fuel. This is what 737 BBJ does with its 5 or 6 belly tanks. It trades passengers for fuel to increase range. I don't think it's impossible to create the Long Range version of 737-10, but perhaps Boeing thinks it's not feasible.

@ParadigmPilot The BBJ is a lot shorter and does not have the rotation limit. The referenced sentence is in connection to the rotation limit. The BBJ has an easy life, weight-wise, with its low payload. The 737-10 is designed to match the range of the A321NeoER, by taking away the rotation limit through a re-design of the landing gear.

@Koyovis: Why not add fueltanks symmetrically to the front and rear of the cargobay, thereby gaining extra fuel without shifting the 737M9's CG?

@Vikki With the same wing, extra TO weight will imply a higher rotational angle at TO - which is the variable that is limited in the B737-9

@Koyovis: Not if you increase VR to compensate for the increased weight, like you do to compensate for heavy cargo and passengers.  If the rotation limit isn't an issue for a particular weight of cargo, it also shouldn't be an issue if some of that cargo weight is traded 1:1 for extra fuel.


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What is the meaning of these stencils, usually found on military planes?
I am wondering what these markings (which I found both in the French Super Etendard and in the British Tornado) indicate? They may be something relevant for the maintenance crews.

The top one indicates that it is safe to hang your uniform jacket from the winglet. :)


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Anticollision beacon light flash frequency, and relationship to strobe lights, for the Embraer E195LR
This question is very similar to one about the A340, but I wonder instead about the following regarding the Embraer E195LR:

Does the anticollision beacon light on top of the fuselage flash at fixed rate for all E195LRs, or could there be changes due to parts replacement?
If yes to the former, what is that flashing frequency? (Regulations give wide ranges for the allowable flash frequency)
Is there a fixed pattern relating that light to the aircraft's strobe lights? (Cf. comments to the A340 question)

(The "asking good questions" page for Aviation SE encourages explanations as to why the question/answer might be useful to others: In my case, I'm attempting to do some temporal synchronization based on (incidental) observation of said light.)

I have one idea for you; you can get videos of that plane on YouTube and count the flashes or do something similar to get the frequency.